The process industry works at times with media, which established elastomers can only conditionally withstand. It is, consequently, usual, in the case of media-contacting seals not to use otherwise usual elastomers, in case such media can be expected. Instead, metal seals or inert synthetic materials, especially fluoropolymers, such as, for example, PTFE, FEP or PFA, are applied. Designs of the components to be sealed relative to one another must then be adapted to the special properties of the sealing materials. Thus, for example, metal seals require, as a rule, large clamping forces, in order to generate the required compressive pressures, and fluoropolymer seals must be elastically prestressed, in order to be able to overcome thermal expansion differences between the, usually, metal sealing partners and the seal itself, thermal stresses in the structure, loosening of screwed joints and, in given cases, hysteresis phenomena associated with the aforementioned effects as well as flow of the sealing material and manufacturing tolerances.
A problem for industrial process measurements technology resulting from this picture is that measuring devices should be suitable for the most varied of process media using an as small as possible number of variants as regards construction. Since, most often, elastomeric seals suffice, it is not justified to provide all devices with such complex construction that they can sufficiently elastically prestress thermoplastic seals.
The yet unpublished German patent application, DE 10 2012 004 406, discloses a metal sealing ring having a z-shaped cross section, wherein the sealing surfaces on the end faces of the sealing ring are coated with a polymer, especially PTFE. The z-shaped cross section effects an axial elasticity of the sealing ring, with which the sealing surfaces can be axially prestressed. The described metal sealing ring leads, however, to temperature dependent fluctuations of the axial clamping forces. Additionally, the manufacturing of the metal sealing ring is expensive.